The supply of fluidizing air to fluid bed furnaces can occur in many different ways. In some embodiments a number of nozzles are used, which project from a plate forming the bottom of the furnace. These nozzles are formed as upwardly closed lengths of tubes, which have air dispersing openings in their shells.
The fluidized bed material, which beside particles of fuel, includes sand and/or crushed limestone, will subject the projecting nozzles to a hard wear, which makes continued repair work necessary.
An additional trouble is that the fitting of the nozzles to the plate is regarded as a qualified work, which must be performed by a licensed welder.
The object of the present invention is to design the individual nozzle so it obtains a high degree of wear resistance, and is generally so formed that--when a survey is required--a substantial part of a nozzle may be rapidly substituted by a new wear-resisting component, without much work.